1. Field of the Invention
The present general inventive concept relates to an inkjet image forming apparatus and a method to control the same with an improved maintenance operation of a print head.
2. Description of the Related Art
Recently, attempts have been made to implement high-speed printing using a line printing type inkjet head (array inkjet head), including a nozzle portion having a length in a main scanning direction corresponding to a width of a print medium, instead of using a shuttle type inkjet head. The inkjet head of this inkjet image forming apparatus is fixed on a main body thereof while the print medium is moved in a sub-scanning direction. Thus, the inkjet image forming apparatus has a simple drive unit and can achieve the high-speed printing.
If some nozzles are clogged or a direction of jetting is changed due to foreign substances, it is difficult for the array inkjet head to compensate for these problems since the array inkjet head jets ink at a fixed position, in contrast to the shuttle type inkjet head which reciprocates in the main scanning direction. Thus, it is necessary to perform an efficient maintenance operation on the array inkjet head.
In order for the inkjet image forming apparatus to print high-quality images, a nozzle portion of the inkjet head must be kept in an optimal state, regardless of whether it is of the shuttle or line printing type. To accomplish this, the inkjet image forming apparatus includes a maintenance device to maintain and keep the nozzle portion of the inkjet head in a normal state. The inkjet image forming apparatus generally performs a maintenance operation such as spitting, wiping, and capping through the maintenance device. Here, the term “spitting” refers to jetting ink a number of times at regular time intervals to remove highly viscous ink, the term “wiping” is referred to as wiping off foreign substances from the nozzle portion, and the term “capping” is referred to as providing a cover for the nozzle portion to separate it from the external air.
The nozzle portion of the inkjet image forming apparatus is maintained in a good (clean) state through the maintenance operation. However, in some cases, the nozzles may be seriously clogged, making it difficult to recover the nozzle portion. To solve this problem, inkjet image forming apparatuses include a cleaner using supersonic waves as a part of the maintenance device.
A conventional method to restrict maintenance is to perform maintenance according to the count of dots corresponding to the amount of printing or according to an off time during which a print job has been suspended. To accomplish this, dots are counted for each print job or an off time taken until a print job is resumed after the print job is suspended is counted and spitting and wiping is sequentially performed when the count has reached a threshold set to a value at which maintenance is performed.
The threshold may be affected by the ambient environment of the inkjet image forming apparatus since the threshold is determined from tests. The threshold at which maintenance is performed may be set to be too low or too high depending on the installation environment of the inkjet image forming apparatus. When the threshold is too low, maintenance may be performed more frequently than needed, which increases power consumption and also causes inconvenience that any print job cannot be actually done while the maintenance is performed. On the other hand, when the threshold is too high, a print job may be performed with some nozzles clogged, thereby reducing the print image quality.
The conventional inkjet image forming apparatus performs maintenance regardless of the actual states of nozzles since it uniformly sets the time to perform maintenance of the head in the above manner.